The present invention relates to a sensor for automotive vehicles with electronic control of or with an electronic system influencing the vehicle's behavior, and in particular vehicles with control of the vehicle's driving and braking behavior and/or vibrational damping. Such control is applied in dependence on the rotational wheel speed and on the vertical acceleration of the wheel or of the wheel suspension, or alternatively on the acceleration of the vehicle body.
Electronic control units for different variables relating to vehicular dynamics have already found their way into automotive engineering. Electrical control of negative wheel slip prevents locking of the vehicle's wheels due to excessive braking pressure, whereby vehicle performance improves considerably during the braking operation. By means of such anti-skid systems, the driving stability and steerability of the vehicle are maintained even on extremely slippery road surfaces or in dangerous situations causing panicky braking operations.
In limiting positive wheel slip by means of electronic traction slip control systems, the start of the vehicle on a slippery road surface is rendered more easy and the driving stability is improved during accelerating operations.
Shock absorbers with an adjustable characteristic damping curve are likewise known. Also, there have already been suggestions of varying the absorber hardness automatically in dependence on kinetic quantities such as vehicular velocity, vertical acceleration and lateral acceleration of the vehicle body. Such variation would be accomplished by means of electrically controllable valves inserted into the connection lines between the working chambers of controllable hydraulic shock absorbers. A substantial improvement in vehicular braking behavior by controlling the absorber hardness is conceivable. Likewise, assisting an anti-skid system-controlled braking operation by changing the absorber hardness would lead to more effective slowing-down and to an improvement in braking comfort.
Further development of such electronic control systems and their large-scale application requires, however, that effective and cheap sensors be available for measuring control variables or for converting kinetic parameters into an electric signal which can be further processed in the logic circuits of a control unit. Parameters which are of particular interest in systems of the type described above are the rotational speed of the wheels and the vertical acceleration of the vehicle body, especially in the area of the vibration absorber.
Magnetic and magnetoresistive transducers are known for measuring wheel speed and rotational behavior. In these transducers, a toothed disk rotating along with the wheel generates an alternating signal either by magnetic induction or by causing a cyclical resistive change. Vertical vehicle body acceleration, on the other hand, can be determined by means of an inertial mass whose relative displacement with respect to a component coupled with the vehicle body is ascertained.
Thus, according to the prior art, a plurality of sensors is required at each wheel. The manufacturing costs, as well as expenses for installation and adjusting of the sensors and related equipment such as connection cables, are therefore rather high. Another disadvantage is the excessive space required for a plurality of sensors, especially since in practice there are but a few points on the wheel suspension that are deemed ideal or even suitable for placing the sensors.
It is thus a general object of this invention to overcome the described disadvantages and to considerably reduce the required manufacturing expenditure and efforts. The reliability of the sensors should to be increased or at least maintained.